A 93-year-old woman has died at the ill-fated Newmarch House aged-home in Sydney, taking the nation’s death toll from the coronavirus to 100.

The woman is the 19th person to die at Newmarch House, near Penrith, the 49th victim of COVID-19 in NSW and the 100th person to die across Australia.

The death comes as three Melbourne aged-care facilities were in lockdown on Tuesday after residents tested positive, then negative, to coronavirus.

Hammond Care nursing home at Caulfield, in Melbourne’s south-east, went into lockdown on Monday after a resident in its dementia facility tested positive to COVID-19, before a second swab came back negative.

General manager Angela Raguz said the home was treating the patient as a positive case while the Department of Health investigated.

“We’re erring on the side of caution,” she told 3AW radio on Tuesday, noting all staff were being tested.

“We’re up in the air a little bit, to be honest.”

Victoria’s deputy chief medical officer Annaliese van Diemen said “a subsequent negative test doesn’t negate the first positive test”.

“We work closely with our laboratory colleagues, and any positive test is considered to be a positive test,” she said on Tuesday afternoon.

On Monday, Newmarch House operator Anglicare admitted it would have been easier if those infected at the the home had been transferred to hospital rather than treated on-site.

But NSW Health stood by the response to the outbreak, given numerous elderly and frail people were involved with serious comorbidities.

Some 37 residents and 32 staff at Newmarch House near Penrith have contracted COVID-19 after a staff member worked for six days with mild respiratory symptoms. It is one of Australia’s worst coronavirus clusters.

Anglicare chief executive Grant Millard said the organisation complied with NSW Health’s containment strategy after the outbreak and anyone who wanted to be hospitalised after contracting COVID-19 was accommodated.

Other residents have been isolated in their rooms and treated inside the facility.

But Mr Millard said protocols around personal protective equipment and infection control would have been far simpler to follow in a hospital setting.

“If I had my time again, I’d be insisting people who are COVID-positive go to hospital – in hindsight that would have been my preference,” Mr Millard told ABC radio on Monday.

“PPE, infection control practices … these are things much better established, bread-and-butter business, in a hospital setting. Trying to do that in a residential aged care setting is complex.”

Mr Millard said 66 staff members had been withdrawn from the facility due to contact with early COVID-19 cases, meaning those working with residents were recruited from elsewhere.

This made communication with families extremely difficult.

“We were scrambling for staff just to provide patient care and just didn’t do a good enough job communicating to families,” Mr Millard said.

“We really had foreign people in the home and they didn’t know (them).”

But NSW chief health officer Dr Kerry Chant stood by the decision-making of clinicians on-site at Newmarch House, saying the situation was complex.

“For many of the residents, that was their actual place of residence … when you move people from their environment they’re exposed to other risks such as falls risk, disorientation and then as a consequence get other health issues,” Dr Chant said.

-with AAP